C：从u_char *解析子字符串

Question

我正在努力寻找u_char *中子字符串的开头，正在尝试获取“ q =”的位置来解析URL中的google搜索。这让我发疯了，如果有人可以帮助我，我将不胜感激。 我的C语言知识有限。

这是我停留在的行： if(g_start = strstr(final_url, "q=") != NULL){

这是我的代码的一部分：

int  url_length,host_length, search_length;
u_char *url, *end_url, *final_url, *host, *end_host, *final_host, *ghostUrl, *google, *g_end, *g_start;


/* copy  host + url to a null terminated c string */
final_url = (u_char*)malloc(url_length + 1); //malloc ( length )  +1 for \0
final_host = (u_char*)malloc(host_length +1);
strncpy((char*)final_host,(char*)host, host_length);
strncpy((char*)final_url, (char*)url, url_length);
final_url[url_length] = '\0'; //null terminerer
final_host[host_length] = '\0';

    /* Everything above works fine.. */
   /* final_url looks like this: /search?biw=320&bih=570&tbm=isch&sa=1&ei=M0eFUsXvHOO54AS644GYCQ&q=dogs&oq=dogs&gs_l=mobile-gws-serp.12...0.0.0.1991659.0.0.0.0.0.0.0.0 */

if(strcmp("www.google.no", final_host) == 0){ /* host: www.google.no */
    if(g_start = strstr(final_url, "q=") != NULL){ /* This fails.. */       
printf("debug: search starts at %s\n", g_start); /* I have no idea.. how to get integer position from strstr()  */
    g_end = strchr((char*)g_start,'&'); // ?q=dogs[&]
    search_length = g_end - g_start;

    printf("DEBUG:  search_length: %i\n",search_length);
    google = (u_char*)malloc(search_length +1);     
    strncpy((char*)google, (char*)g_start, search_length);
    google[search_length] = '\0'; //null terminator

Answer 1

运算符优先级意味着

if(g_start = strstr(final_url, "q=") != NULL)

被评估为

if(g_start = (strstr(final_url, "q=") != NULL))

它将为g_start分配1或0 。

您需要在行的开头使用括号() ，以获得所需的求值顺序：

if((g_start = strstr(final_url, "q=")) != NULL)
// ^                                 ^

请注意，您的编译器应已对此发出警告。 例如MSVC给

warning C4047: '=' : 'char *' differs in levels of indirection from 'int'